NBD-Cl is non-fluorescent, and generates fluorescent products upon reacting with aliphatic amines or thiol compounds. It reacts with amino groups such as aliphatic amines, amino acids, peptides, and proteins to form highly fluorescent compounds. The fluorescence spectra of NBD-amine adducts are highly environment-sensitive, the fluorescence intensity decreases significantly in aqueous solutions. The NBD-amine adducts have l­­ex = 464 nm and lem = 512 nm in aqueous solutions. NBD-Cl also reacts with thiol group to form fluorescent adducts. NBD-Cl is widely used to label peptides, proteins, drugs and other biomolecules. It is also a popular derivatizing reagent for HPLC analysis.